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The best police work usually involves the liberal application of shoe leather, whether the perps are thugs or bugs.

That turned out to be the case for one eatery, where "textbook epidemiological process" discovered that recurring food poisoning didn't arise from the food.

Since June of this year, an International House of Pancakes restaurant in Amarillo, Texas, has been closed down no fewer than three times with recurrent salmonella infections.

Between Father's Day and early July, the restaurant was responsible for 90 reported salmonella infections. Health authorities shut it down the first time on July 15 and again eight days later. When the local public health officials tested 68 employees, 11 tested positive for salmonellosis. Corrective measures included instructions with workers on hand-washing and food-safety measures, but the problem didn't end.

The IHOP closed a third time in mid-September when seven more cases of salmonella were linked to the eatery. Baffled by the persistent recurrence of the illness, public health officials took a closer look at the interview reports.

"We were truly the disease detectives," said Deree Duke, director of the Environmental Health Department at the Amarillo Bi-City-County Health District. "When we discovered the last group of people had all eaten pancakes, we thought we were on to something. We asked people what else they had eaten, and we tested mixes, eggs, other potential sources. But these were all dead ends, so we knew it was something else associated with eating pancakes."

Duke explained that a classic epidemiology investigation connects the dots between individuals who are ill and shared exposure to places, food or other events, looking for the common source — the "reservoir" — of disease. Finding the reservoir of illness arising from a single location should simplify the task, but Duke said this investigation had to dig deeper than usual.

"This was a collaboration between the public health officials who interviewed and analyzed the data and the sanitarians, who carefully collected samples and ran the laboratory analyses." When they looked at the client interviews again and talked to the "pancake people," the key clue emerged.

"One man said he looked at the maple syrup bottle and saw a thin layer of clear liquid floating on top, so he chose boysenberry.

"We decided it may have something to do with the syrup toppings, so we tested everything and swabbed for cultures again, this time including the hot-water bath used for storing the syrup bottles."

When the water bath tests came in positive for salmonellosis, "We knew we were on to it," Duke said. The patrons' type of salmonella and that from the water bath matched exactly.

"Tests of the syrup itself also were positive. So, not only was the water bath contaminated; the bacteria migrated into the bottles through handling, and in some cases, the water itself got inside the bottles, which accounts for the report of 'a thin layer of fluid' described."

The IHOP was reopened this week, and the syrup hot-water bath has been discontinued; Duke said a microwave will be used.

According to the International Society for Infectious Diseases, the discovery of this water bath contamination as a "novel transmission vehicle" for illness reminds us that "food itself is not always the reservoir of disease."

Duke said their work only underscores the continuing need for "good old-fashioned interviewing techniques by people who are trained to listen for and match the clues needed to solve these kinds of public health mysteries.

"It was very cool that our hypothesis matched our findings!"

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